Al-Qaida inspired British Islamic extremists Ashik Ali, Irfan Khalid and Irfan Naseer who were found guilty of plotting a campaign of bombings in crowded areas. Photograph: Handout/Reuters

Three would-be suicide bombers face life in jail after a jury convicted them on Thursday of plotting to carry out terror attacks in the UK which would have been more deadly than the 7/7 bombings in 2005.

The men from Birmingham are the latest group of British-based extremists to be radicalised by the preachings of the now-dead Anwar al-Awlaki, the one-time leader of Al-Qaida in the Arabian Peninsula.

His extremist message continues to be spread from beyond the grave through the English language terror manual he created, Inspire magazine, which is still disseminated via internet forums despite robust attempts by the security services in the UK and abroad to stop it. Videos of sermons by Awlaki were still available late Thursday on YouTube.

The men's plans to create their own 9/11 by making bombs from sports injury cold pack treatments were thwarted by the biggest counter-terror operation mounted in the UK for seven years, which at times involved more than 400 officers and agents.

Convicted on Thursday by a jury at Woolwich crown court, London, of engaging in conduct in preparation of terrorist attacks, the three were key figures in a terror cell in the Sparkhill area of Birmingham. They aimed to detonate eight to 10 suicide bombs and timed explosive devices that prosecutors said could have caused "death and injury on a massive scale". Six other members of the cell had earlier pleaded guilty.

The ringleaders, chemistry graduate Irfan Naseer, 31, and Irfan Khalid, 27, both from Sparkhill had travelled to Pakistan twice for training – on the second occasion spending two months at an al-Qaida training facility in Miran Shah, in north Waziristan, where they had to flee from American drone strikes. They recruited Ashik Ali, 27, from Balsall Heath in Birmingham, on their return, and began to draw others into the plot.

They duped members of the public into donating thousands of pounds to fund their terror plot by posing as collectors for the charity Muslim Aid in Sparkhill. Within two weeks they raised £14,500, which they diverted to fund their activities.

Police in the West Midlands defended the reach of the government's multimillion pound anti-terror strategy, Prevent, at the conclusion of the trial. Despite millions of pounds being spent in the Sparkhill area relatives and friends of some of those involved who became suspicious chose to take action themselves rather than pass information to the police.

Mr Justice Henriques told the guilty men it was clear they were planning to carry out a spectacular bombing campaign and that they would all face life in prison when they are sentenced in April or May. Speaking to Naseer, the judge said he had been convicted on "overwhelming evidence" and that he would face "a very long minimum term".

He said: "You are a highly skilled bomb maker and explosives expert. Your mindset was similarly manifest. You were seeking to recruit a team of somewhere between six and eight suicide bombers to carry out a spectacular bombing campaign, one which would create an anniversary along the lines of 7/7 or 9/11."

Khalid he said was was "very much his (Naseer's) confidant and his right-hand man."

Of Ali, the judge said he "intelligent, devious and highly manipulative."

Marcus Beale, assistant commissioner of West Midlands police, who worked with the security services to intercept the plot, said: "This group was critical of the 7 July bombers because they didn't kill enough people. If they delivered on the plans that they had they would have committed mass murder on a horrendous scale."

However, there was evidence that the men were struggling to get the ingredients for their plot and no targets were identified by the police or security services. When arrested they were found in possession of just one sports cold pack kit which did not contain the key ingredient for the bombs, ammonium nitrate, because the substance is no longer used in the products.

Beale defended the role of Prevent. Relatives and friends were aware that four followers of Naseer, Khalid and Ali had travelled to train in Pakistan in 2011, but instead of contacting the police they successfully used their own contacts in the country to get the men to return home.

Beale said: "It would be fantastic if more information would come from the community. But if my child was going off the rails I would definitely be wanting to help them myself first rather than go the police and any parent would want to do the same so I would not want to be critical."

Naseer and Khalid built their plot on their return from the training camp in Miran Shah, in the summer of 2011. They shared their knowledge of bomb making with Ali, who rented a council flat which became a makeshift bomb factory and the hub of the plot. Experts told the court they could have created a viable device.

But unknown to the men they were being watched by the police and security services who had placed bugs in two cars and the bomb factory which picked up the plot being described as another 9/11.

At one point the three men were heard driving in a car mimicking Formula One commentator Murray Walker, and joking: "It's the four suicide bombers driving around ready to take on England."

Khalid also said of the plot: "This is going to kick them all, the [infidels] that go to the pub and that; they have hit us in our own country, my God they hit us."

Naseer was found guilty of five counts of engaging in conduct in preparation of terrorist attacks, Khalid of four and Ali of three counts – all between Christmas Day 2010 and 19 September 2011.

They are the latest group of British-based extremists to take their inspiration from American-born Awlaki, the Yemen-based cleric who was a leader of AQAP until he was killed by a US drone in September 2011.

Other extremists who have used his sermons and Inspire magazine to self-radicalise include Roshonara Choudhry, who attacked the MP Stephen Timms, and four terrorists from Birmingham who were convicted in 2012 of plotting to blow up the London Stock Exchange. A search of Ali's house after his arrest uncovered a vast library of lectures by Awlaki.

One of the plans discussed by the three – of attaching blades to the wheels of cars in order to mow down pedestrians – came directly from Inspire, the second edition of which describes how to create "the ultimate mowing machine".

Sue Hemming, head of special crime and counter-terrorism in the CPS, said: "A considerable number of investigations have uncovered connection to and support for the teachings of … Awlaki...his pernicious and hateful views unfortunately live on in his recorded speeches and Inspire magazine."

Keith Vaz MP, chair of the home affairs committee, criticised YouTube over Awlaki material being on the site. "Youtube should not be hosting this material. Material which incites violent radicalism should not be on Youtube. They should be much more proactive in taking it down without waiting for complaints."

Azad Ali, chair of the Muslim Safety Forum which has worked with the police to combat Jihadi violence, said that if Awlaki material was found in a book shop a proseuction wouldme made, saying: "Youtube is hosting the same material and there seems to be no action taken against it at all..

YouTube said: "YouTube has Community Guidelines that prohibit dangerous or illegal activities such as bomb-making, hate speech, and incitement to commit violent acts, and we take violations of these guidelines seriously. Our review teams respond to flagged videos around the clock, routinely removing material under those policies. Our flagging tools include a flag labeled "promotes terrorism" to make it easier for our users to identify content that incites violence."